This invention relates to a method for labeling or tagging a biological compound or structure with a metal or semiconductor particle and the structures produced by such methods. Conventional techniques for producing nanoparticle tags for spatially locating proteins are not compatible with retaining normal structure or with in-situ use. Traditionally, quantum-dot conjugates bound using, for example, streptavidin are larger than most proteins and the tagging process may interfere with biochemical processes and seriously distort the biological structures that one wishes to study. These methods also require modification of the protein target, for example, biotinylation, to enable binding of the tagging particle; this can disrupt the normal behavior of the target even before attachment of the tag. Since quantum dots are typically 10 to 25 nm in effective diameter, the distortion and interference resulting from their excessive size will frequently preclude their use in applications where retaining the activity or structure of the protein is desired.